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carpal trochlea relatively small (carpometacarpus larger,
metacarpal I relatively smaller, with distinct proximal curvature,
fossa below pisiform shallow and broad, area of internal
ligamental fossa relatively greater in Amplibuteo woodwardi
(«=4) and A. hibbardi). Coracoid with relatively short, narrow
coraco-humeral surface (long and broad in A. woodwardi
{n=5), short and broad in .4. hibbardi); pneumatic foramina below
brachial tuberosity small and indistinct (shallow to deep in
A. woodwardi). Humerus (Figure 3) with internal tuberosity
relatively narrow and less blunt (large and blunt in A. woodwardi
(«=9), rounded in A. hibbardi); distinct excavation at
distal end of medial bicipital crest (deep in A hibbardi; deep to
shallow or absent in A. woodwardi); ligamental furrow relatively
narrow and deep (furrow broad, shallow to deep in A.
woodwardi); bicipital crest merges with shaft immediately below
pneumatic foramen (merges with shaft more distal to pneumatic
foramen, forming a distinct flange, in A. woodwardi and
A. hibbardi); attachment for anterior articular ligament relatively
flat, long, and narrow (flat to convex, short and broad to
long and narrow in A. woodwardi, short and rounded in A.
hibbardi); impression of M. brachialis anticus relatively narrow
(broad in A. woodwardi); and entepicondylar and ectepicondylar
prominences relatively small (larger and more robust
in A. woodwardi). Ulna with bicipital attachment relatively
high on shaft (attachment more distal on shaft in A. woodwardi
(«=3) and A. hibbardi); prominence for anterior articular ligament
relatively small (large and robust in A. woodwardi and A.
hibbardi); distal external condyle relatively long and narrow
(short and broad in A. woodwardi and A. hibbardi); and carpal
and radial tuberosities prominent (reduced in A. woodwardi,
more prominent in A. hibbardi). Radius with ligamental prominence
relatively small and blunt (large with more distal extension
in A. woodwardi («=2) and ,4. hibbardi); scapholunar facet
in distal view relatively short and narrow (long and broad in
A. woodwardi).
COMPARATIVE MATERIAL.—Morphnus guianensis (Daudin),
skeleton, USNM 432243, unsexed; LACM 91788, skeleton,
female. Harpyhaliaetus solitarius (Tschudi), partial skeleton
with sternum, coracoid, proximal humerus, and femur,
UCLA 41971, unsexed.
STATUS.—Extinct, known from fossils only.
REMARKS.—The material from Haile 7C is probably from a
single individual based on similarities in the size and features
of matching elements. At least one individual is represented
from Inglis 1C, and the humerus (UF 165542) is slightly porous
and incompletely ossified, indicating it is from a subadult.
Amplibuteo concordatus was a small eagle compared to A.
woodwardi ox A. hibbardi. A third possible species of Amplibuteo
(UF 102550), reported by Emslie (1995) from the late-early
Irvingtonian Leisey Shell Pit 3B, is slightly larger than A.
concordatus and smaller than A. woodwardi (see measurements
in Emslie, 1995, table 11). It compares most closely with
A. woodwardi except for the carpometacarpus, which is shorter
and differs in characters as described by Emslie (1995). The
carpometacarpus (UF 102550) from Leisey was compared with
UF 159426 and AMNH 10395 and was found to differ in having
a distinct proximal curvature of metacarpal I and having the
fossa below the pisiform process broad and deep. These differences
also suggest that the Leisey specimen represents a fourth,
undescribed species of Amplibuteo.
Of the two other fossil species described in this genus, A.
woodwardi is known from the late Pleistocene of Rancho La
Brea, California, and the middle and late Pleistocene of Florida
(Miller, 1911; Howard, 1932; Emslie, 1995); A. hibbardi is
known only from the late Pleistocene Talara Tar Seeps, Peru
(Campbell, 1979). The addition of A. concordatus to this
record extends the geologic range of the genus into the late
Pliocene. This species also was relatively long-lived, with a potential
geologic range spanning 2.1 million years (between
3.7-1.6 Ma). The genus reached its greatest diversity in the
Pleistocene of North and South America, when up to three species
may have existed, although none of these apparently were
sympatric based on the available evidence.
Campbell (1979) erected the genus Amplibuteo, with A. hibbardi
of Peru as the type species, and at the same time transferred
the fossil species Morphnus woodwardi from Rancho La
Brea to the same new genus. His comparisons suggested that
Amplibuteo is most closely related to Buteo and Geranoaetus,
whereas Morphnus is closer to Harpia than to other genera.
Campbell's comparisons included one specimen of Harpyhaliaetus
solitarius, from which only the tarsometatarsus was
used in the generic diagnosis of Amplibuteo. We compared the
sternum, coracoid, proximal end of the humerus, and femur of
this species with those of Morphnus guianensis, Amplibuteo
woodwardi, and A. concordatus. These comparisons indicate a
closer similarity in skeletal characters between Harpyhaliaetus
and Amplibuteo than previously has been recognized. Characters
shared by these two genera include the sternum with the
anterior carinal margin placed relatively far from the manubrium,
the coracoid with the coracoidal fenestra positioned relatively
far from the scapular facet, the humerus with a bicipital
crest that merges with the shaft distally, giving the crest a distinct
flange in A. woodwardi (although the crest merges immediately
to a shaft with no flange in A. concordatus and Harpyhaliaetus),
and the femur with a high trochanter and a
trochanteric ridge extending far down the shaft.
These similarities raise the possibility that Amplibuteo may
be closely related to or even congeneric with Harpyhaliaetus,
of which additional modern skeletal specimens would be highly
desirable. The high diversity of Accipitridae and the lack of
adequate comparative skeletons for some species (e.g., H. coronatus),
however, compound the problems associated with describing
new taxa in this group, and additional, more detailed
comparisons are needed with all accipitrid genera. The two
species of Harpyhaliaetus are today confined to the Neotropics.
The Crowned Solitary Eagle {H. coronatus) is found in
savannah habitats from Bolivia to southern Argentina, whereas
the Black Solitary Eagle {H. solitarius) occurs on mountain